1. Field of the Invention
The present invention relates to a display module, and more particularly, to a liquid crystal display module.
2. Description of the Related Art
In general, liquid crystal display module (LCM) devices have been incorporated into various display devices because of their light weight, thin profile, and low power consumption. For example, the LCM devices are commonly used in office automation devices and audio/video devices. The LCM devices adjust light transmission in accordance with images signal supplied to a matrix array of control switches to display desired images into a display screen. However, since the LCM devices are not spontaneous light-emitting devices, the LCM devices require a back light unit to function as a light source.
Two types of the backlight units used for the LCM devices include direct-below-type and edge-type backlight units. The direct-below-type LCM device includes a plurality of lamps arranged below a liquid crystal panel, wherein a diffusion plate is provided between the lamps and the liquid crystal panel to diffuse the light produced by the lamps and to maintain a uniform gap between the lamps and the liquid crystal panel. The edge-type LCM device includes a lamp installed along an edge of a light-guide plate to irradiate light to the liquid crystal panel via the light-guide-plate.
FIG. 1 is a cross sectional view of direct-below-type back light unit according to the related art. In FIG. 1, a direct-below-type back light unit includes a plurality of lamps 12 placed parallel with each other for generating light, a lamp housing 10 for accommodating the lamps 12, a diffusion plate 14 covering an open portion of the lamp housing 10, and a diffusion film 16 and a dual brightness enhancement film (DBEF) 18 stacked sequentially on the diffusion plate 14. Each of the lamps 12 comprises a glass tube filled with inert gases, and a cathode and an anode installed at opposite ends of the glass tube. In addition, inner walls of the glass tube are coated with phosphor material.
FIG. 2 is a schematic perspective view of a lamp of FIG. 1 according to the related art. In FIG. 2, when alternating current from an inverter (not shown) is supplied to a high voltage electrode H (i.e., first envelope) and a low voltage electrode L (i.e., a second envelope) of each lamp 12, electrons are emitted from the low voltage electrode L. Accordingly, the emitted electrons collide with the inert gases contained within the glass tube, wherein a number of the electrons exponentially increases. Next, the increased number of electrons generate electric currents within the glass tube, thereby exciting the inert gases to emit ultraviolet light. Then, the ultraviolet light collides with the phosphor material coated on the inner walls of the glass tube, thereby generating visible light.
In FIG. 1, the lamp housing 10 prevents leakage of the visible light radiated from each of the lamps 12, and reflects the light incident to sides and rear surfaces of the lamp housing 10 toward the diffusion plate 14 positioned at a front of the lamp housing 10, thereby increasing light radiation efficiency of the lamps 12. In addition, reflection plates (not shown) are formed on a bottom surface and the sides of the lamp housing 10. The diffusion plate 14 diffuses the light radiated from the lamps 12 toward the liquid crystal panel over a wide range of incident angles. The diffusion plate 14 includes a transparent resin film having opposing surfaces coated with light-diffusion material. Accordingly, the diffusion film 16 and the DBEF 18 increase a diffusion efficiency of the light transmitted through the diffusion plate 14. An LCM device employing the direct-below-type back light unit is commonly used for large-screen televisions. However, as shown in FIG. 1, lamp housing 10 has a relatively large depth L1.
FIG. 3 is a cross sectional view of another direct-below-type back light unit according to the related art. In FIG. 3, a direct-below-type back light unit has a plurality of scattering printed patterns 20 on the rear surface of the diffusion plate 14. Accordingly, the scattering printed patterns 20 are formed at designated intervals to scatter the light generated from each of the lamps 12. Due to the scattering effect by the scattering printed patterns 20, it is possible to decrease a depth L2 of the lamp housing 10 be less than the depth L1 of the lamp housing 10 of FIG. 1.
The scattering printed patterns 20 decreases the gap between the diffusion plate 14 and the lamps 12 to create a uniform brightness. In addition, the depth L2 of the lamp housing 10 decreases an overall thickness of the direct-below-type back light unit. However, the light radiated from adjacent lamps 12 and scattered by the scattering printed patterns 20 is partially overlapped, thereby increasing the brightness at the overlapped portion. Thus, the brightness is not uniform.
FIG. 4 is a cross sectional view of another direct-below-type back light unit according to the related art. In FIG. 4, a direct-below-type back light unit includes a plurality of protrusions 24 that project from the bottom surface of the reflection plate 22 toward the lamps 12 inside the lamp housing 10. The protrusions 24 of the reflection plate 22 are formed having a triangular form and are disposed within every gap between the adjacent lamps 12. The protrusions 24 prevent interference of light between the adjacent lamps 12 and increase brightness uniformity.
In addition, the protrusions 24 reduce the gap between the diffusion plate 14 and the lamps 12 to create a uniform brightness. Accordingly, a depth L3 of the lamp housing 10 reduces a thickness of the direct-below-type back light unit. However, in order to further reduce the thickness of the direct-below-type back light unit, the geometric shape of the reflection plate 22 must be changed.